In a conventional package-on-package (POP) process, a top package, in which a first device die is bonded, is bonded to a bottom package. The bottom package may also have a device die packaged therein. By adopting the PoP process, the integration level of the packages may be increased.
In an existing PoP process, a bottom package is formed first, which comprises a device die bonded to a package substrate. A molding compound is then molded on the package substrate, wherein the device die is molded in the molding compound. The package substrate further comprises connectors that are on the same side of the package substrate as the device die. The connectors are used for connecting the bottom package to a top package. Through-molding openings are then formed in the molding compound, so that the connectors are exposed through the through-molding openings. In the formation of the through-molding openings, laser drill is used to remove portions of the molding compound that cover the connectors. After the laser drill, however, the molding compound residue may be left on the surfaces of the connectors.